The topic at hand is Kant’s argument for the claim that all changes that occur in nature are subject to the law of the connection of cause and effect. Kant makes this claim and gives the argument in the “Second Analogy” section of the Critique of Pure Reason. The aim of this discussion is to present a summary of key elements of his extended argument, which seeks to prove the existence of a general and objective cause and effect.
Kant begins by stating the obvious: we perceive appearances, and we perceive changes in those appearances, and these changes and appearances seem to succeed one another. He reminds the reader that changes in appearance represent varying states that occur in some sense “over” an eternal substance, without reflecting a change in the “being and not-being” of the substance itself – “substance” in the deepest sense is altered, not destroyed and remade (B232-233). In more contemporary parlance, we might know this as the law of conservation of mass and energy. Kant says that the connection between these perceptions is indeed real, but it is not something determined by perception by way of sensibility or intuition – instead, it is determined according to a synthetic judgment between the perceptions (by the imagination) (B233).
However, this determination by way of judgment is merely relative to the person making it; the judgments about the appearances reflect a person’s inner sense of time, and his ordering of perceptions according to it, and do not immediately show an objective relation between those appearances, much less any kind of necessary objective relation in nature. The objective relation of cause and effect should show that one whatever came first determined the thing(s) that would follow; in this section, Kant hints at his solution by saying that “experience is possible only by our subjecting the succession of appearances…to the law of causality; and appearances themselves, as objects of experience, are consequently possible only in accordance with this law” (B234). Yet this still seems merely descriptive. Is Kant only asserting that our ordering of appearances requires that such an order be objectively real, that this ordering must therefore have some sort of objective reality with regard to the objects of experience? Not precisely.
He goes on to address this, or at least, reference it as a distinction he is aware of – while it is readily apparent that our perceptions of change or alterations is successive, implying a cause and effect, we can still be skeptical about whether this reflects anything in the objects themselves (B235). This seems to be a red herring; what we call appearances of objects (synthesized and apprehended as a manifold) are to be taken as representations which are themselves objects of consciousness. We are not transgressing any kind of transcendental boundary, but making instead judgments about a manifold which is, as far as humans are concerned, always taken together and presented entirely in the mind, through sensibility. We are not making any claim about “things in themselves” – Kant says that this investigation would be futile if we were. Further, he insists that we “always deal only with our representations; how things may be in themselves…is completely beyond the sphere of our knowledge” (B235). This introductory section is key to the picture Kant paints in the argument, because it frames his discussion in such a way as to avoid Hume’s objections to merely inductively derived causality – Kant’s law is to be derived as a function of the “formal conditions of empirical truth,” as a “necessary rule of apprehension” (B236).
Kant claims that the subjective succession observed in human experience must be derived from the objective succession because otherwise the subjective succession would have no consistent orientation – and this objective succession is such because it occurs in accordance with a rule (B238). This rule is the condition of events as such, at least events that are possible to be referred to in experience, that is, events that occur as phenomena that are accessible to human sensibility. Kant calls us to imagine that this were not the case, and says that it seems without such a rule – a real rule – by which successions in perception are governed objectively, we could not refer anything in appearance to objects, which means we could not have concepts or intuitions, and in turn, no claim to real knowledge, even of objects of experience (B238-239).
This rule, which relates the succession of appearances to one another and orients experience, is not derived from experience, but recognized in experience, and is known from the fact of experience, i.e., as a condition for the occurrence of that which inarguably occurs (B240-241). We cannot appeal to a particular object, because then we would make a transcendental error (to paraphrase his rather verbose account of what it means to transgress the bounds of pure reason), but we can examine the time-relationship of the manifold of representations given in the synthesis of appearances, and look to objects as they appear within that manifold, in their successive states, as being determined by their antecedent states according to a rule (B242-244).
He posits that there simply is “an order among our representations, in which the present state points to a preceding state which…connects the event with itself necessarily in the series of time” (B244). This would show that we cannot arrive at a succeeding time without passing through a preceding time; in recognizing this, Kant says that we seem to have recognized a formal condition of perception, something that cannot be otherwise than he has explained it if experience is possible. This also shows that any knowledge of an object or an event must include its status as being-conditioned by an antecedent state, which means, of course, nothing less than that there is a causal relation between successive appearances and transitively the objects of experience contained within them (B246-247).
He then addresses a subtle contention regarding the apparent simultaneity of cause with effect; however, it remains that causal relations are always determinable in time. It is nonsensical, with respect to possible human experience, to say that a consequent determined its antecedent (to say that now determined what is past, that a conditioned determined its conditions) even if the time between the two is “vanishingly brief” or if their successive states overlap and blend to some degree (B249). Kant also explains, in strikingly simple terms, how action itself implies a relation of the subject of a cause (we might say agent) to its effect, and that this implies a permanent substance of some kind that undergirds a “subject of cause” – a locus of experience and agency, something we might call a self but that is not the perceived self (B250-252).
This eventually leads to a discussion of time as a continuity in B254 onward, and of a property of causality as its being continuous and persistent, not instantaneous. This discussion of how time and causality function is purely a priori, says Kant, but it still expands our knowledge of nature; it shows what is possible for us to discover about nature by drawing boundaries of possible perception and discourse. After all, time is one of the formal conditions of experience, and all empirical knowledge must be consistent with its properties, so if time determines that there must be a connection between successive appearances as condition and conditioned or cause and effect as an objective rule, then this rule must apply to nature and all changes within nature, since all possible empirical knowledge of nature can only occur in time. Hence this law of cause and effect is rendered objectively valid with respect to those changes (B256).